This is the Real and True Mercy

Imaam Ibn Qayyim stated: 

One of the indispensable things to know is that mercy is an attribute that necessitates transmission of benefits and wellbeing to a servant even if his soul dislikes it and is excruciating to it. This is the real and true mercy. So the most merciful of mankind to you is the one who causes you inconvenience in bringing benefit to you and repelling harm from you. Part of the mercy of a father to his son is to compel him to be well cultured through knowledge and deed, to be hard on him in that regard through beating and similar actions, and to restrain him from his lusts that will cause harm to him. Whenever he fails to do that to his son, it signifies paucity of mercy to his son even if he thinks he is showering him with mercy and making life pleasant and comfortable for him. This type of mercy is associated with ignorance, like the mercy of the mother.

Thus, among the perfection of mercy of the Most Merciful is to inflict various types of calamity on the servant, because He is more knowledgeable of his benefit. Consequently, His afflicting him, testing him and restraining him from many of his goals and desires are from His compassion for him. However, because of the ignorance and transgression of the servant, he will blame his Lord for trying him with calamity without knowing His kindness to him with the test and trial.

It was reported in one narration that: “If a person supplicates for the afflicted by saying:  “O Allah, have mercy on him.” Allah – exalted be He - will say: “How will I show mercy upon him more than how I am presently showing mercy upon him?” In another narration: “If Allah loves His slaves, He shields him from the good things of the world and its passions just as one of you would shield his sick person.” So this is from the perfection of His mercy on him and not because of His stinginess to him. Why would He be stingy when He is the Most Generous, and the One to whom all generosity belongs? The generosity of all the creatures in relation to His generosity is lesser than an atom compared to the mountains and sands of the world.

Among the mercy of Allah on His slaves is that He tested them with obligations and prohibitions out of mercy and protection. He is not in need of them as regards to what He enjoined on them, because He is Rich and Praiseworthy; and not because He is parsimonious to them concerning what He has forbidden them, as He is the Most Generous, Most Bountiful. Another form of His mercy is that He made this worldly life resentful and disturbing to them so that they will not feel at home in it nor find tranquility in it, thus they will be desirous of permanent bliss in His abode and within His proximity. Consequently, He transports them to that through series of test and trials.

So He withheld from them in order to give them; He afflicted them with calamity in order to grant them wellbeing; and He caused them to die in order to give them life. From His compassion to them is that He warned them against Himself so that they will not be deluded and treat Him in a manner not befitting of Him as He said:  “And Allah warns you against Himself (His Punishment) and Allah is full of Kindness to the (His) slaves.” [Soorah Aal-Imraan: 30]. More than one of the pious predecessors said: “Among His kindness to His servants is that He warns them against Himself so that they will not fall into deception with Him.”

Source: Ighaathah al-Lahfaan min Masaa’id ash-Shaytaan by Ibn Qayyim al-Jawziyyah